The present invention relates generally to optical fiber ribbons and to fiber optic cables incorporating at least one such optical ribbon. The present invention relates more particularly to a system for optical ribbon identification.
In fiber optic cables that contain a relatively large number of optical fibers, the fibers are often provided in the form of optical ribbons. For instance, one type of cable in common use comprises a single buffer tube containing one or more stacks of optical ribbons. Each stack of optical ribbons can contain as many as 18 optical ribbons, or even more. In use, a given optical ribbon is separated from the stack and some or all of the individual fibers in the optical ribbon are connected to further devices of the overall system architecture. Accordingly, it is necessary for a worker in the field to be able to pick out a given optical ribbon in a stack.
To this end, techniques have been developed for optical ribbon identification by applying visible markings to the optical ribbons. For instance, one such technique currently in use is to apply indicia to the matrix covering of an optical ribbon, in the form of dots of ink that collectively form characters (i.e., letters and numbers). It has become a standard practice to identify optical ribbons by two pieces of information: ribbon number, and fiber type. More specifically, if a cable contains, for example, 18 optical ribbons, the optical ribbons are assigned numbers from one to 18. Some optical ribbons may contain single-mode fibers while other optical ribbons may contain multi-mode fibers or other types of fibers. Thus, in accordance with the conventional method for identifying the optical ribbons, each optical ribbon is marked with its ribbon number (e.g., xe2x80x9c07xe2x80x9d to denote the seventh optical ribbon) and with one or more additional characters denoting the type of fibers contained in the optical ribbon (e.g., xe2x80x9cSxe2x80x9d to denote single-mode fibers).
One known disadvantage of marking optical ribbons with characters formed by ink dots, as described for instance in U.S. Pat. No. 6,064,789 assigned to the assignee of the present application and incorporated herein by reference, is that the ink dots can produce microbending in the fibers, which can result in an increase in optical attenuation. It would be desirable to reduce or eliminate such increase in optical attenuation caused by application of optical ribbon identifiers. The ""789 patent discloses a technique for applying ink dots in such a way that a lesser increase in optical attenuation is caused thereby. The technique is effective, but still further improvement would be desirable.
In addition to the need to identify and break out individual optical ribbons from a cable, there is sometimes a need to identify and/or break out one or more particular optical fiber sub-units from a given optical ribbon whose optical fibers are arranged into two or more fiber sub-units. For instance, a 36-fiber optical ribbon may have the optical fibers arranged in three sub-units of 12 fibers each. Each sub-unit has a matrix covering that binds the optical fibers together, and another outer matrix covering binds the sub-units together. It is desirable with such an optical ribbon to be able to separate any one of the sub-units from the others, and to have the optical fibers of the separated sub-unit remain bonded together. With existing optical ribbons, it is sometimes difficult to accomplish this task.
Additionally, when separating a fiber sub-unit from an optical ribbon, it would be desirable for the separated sub-unit to retain identifying indicia or other markings enabling the worker to identify the sub-unit. Existing optical ribbons typically have such identifying indicia printed on the outer surface of the outer matrix covering. When separating one such optical ribbon from another in the field, it sometimes happens that the two optical ribbons do not cleanly separate at the juncture between their outer matrix coverings, but instead part of the outer covering of one ribbon remains bonded to the outer covering of the other ribbon. Because of this phenomenon, sometimes referred to as xe2x80x9coverhangxe2x80x9d, the identifying indicia of the one ribbon can be inadvertently stripped off when the optical ribbons are peeled apart from each other, making it more difficult to properly identify the sub-units of the affected ribbon. It would be desirable to provide an optical ribbon facilitating a more-reliable identification of optical ribbon sub-units.
In accordance with one aspect of the present inventions, identifying information about an optical ribbon is conveyed by a series of colored regions visible at an outer surface of the optical ribbon matrix covering. In preferred embodiments of the present invention, the colored regions are formed in such a way that they do not cause microbending or the like.
More particularly, an optical ribbon in accordance with one preferred embodiment of the present invention is identified by providing at least two colored regions visible at the outer surface of the matrix covering of the optical ribbon. At least one colored region is used to distinguish the optical ribbon from other optical ribbons in a given cable. For example, one or more colored regions can be used to denote a number pre-assigned to the optical ribbon; thus, if the optical ribbons in a cable are assigned two-digit identifying numbers, each optical ribbon can have two colored regions denoting the two digits of the optical ribbon number. Of course, if three-digit numbers were used for identifying the optical ribbons, then three colored regions could be used for denoting the three digits. Each colored region preferably has a color that denotes an integer number, in accordance with a predetermined code. For instance, the color black can denote the integer xe2x80x9c0xe2x80x9d, and brown can denote the integer xe2x80x9c1xe2x80x9d. Additional integers can be denoted by other colors.
The type of optical fibers contained in an optical ribbon can be denoted by another of the colored regions. As an example, such colored region can be the color gold to denote multi-mode fibers, or the color silver to denote single-mode fibers. Yet another color can be used to denote another fiber type, such as large effective area fibers, for example LEAF(copyright) optical fibers of Coming Inc.; alternatively, the absence of any color in the colored region for fiber type could be used to denote such additional fiber type.
In preferred embodiments of the present invention, the colored regions comprise stripes formed on or in the matrix covering of the optical ribbon. Advantageously, the stripes extend continuously along the length of the optical ribbon. Alternatively, the stripes can extend transversely across the optical ribbon and can be repeated at periodic intervals therealong. Furthermore, colored regions in shapes other than stripes can be used.
An optical ribbon in accordance with one preferred embodiment of the present invention is provided with identifying colored regions during the process of forming the optical ribbon. The optical fibers are passed through an extrusion tool into which fluid matrix material, typically a UV-curable polymer, is supplied such that a covering of the matrix material is extruded over the fibers. Colored polymer material is also supplied to the extrusion tool through passages formed therein. The colored material can be matrix material to which coloring agents are added, or can be ink or the like. Preferably, the passages are so formed and located that the colored material is injected at a point upstream of the exit portion of the extrusion tool defining the outer profile of the matrix covering. In this way, the colored regions do not form protrusions that could cause microbending in the optical fibers.
As an alternative, the colored material can be applied after extrusion of the matrix covering but before the matrix material is cured, such as in an additional tool. Furthermore, other methods for applying the colored regions could be used, all in accordance with the present invention.
In another aspect of the present invention, separation and/or identification of fiber sub-units in an optical ribbon are facilitated. An optical ribbon in accordance with a preferred embodiment of the invention comprises a plurality of optical fibers arranged generally parallel to one another in a generally planar array, the optical fibers being arranged into at least two fiber sub-units; and an outer matrix covering that encapsulates and binds together the fiber sub-units, the outer matrix covering comprising separate regions of a first matrix material adhered respectively to each of the fiber sub-units and a connecting region of a second matrix material joining adjacent fiber sub-units together. The first matrix material adheres to the fiber sub-units with a greater tenacity than does the second matrix material such that the outer matrix covering preferentially splits at the connecting region between fiber sub-units, whereby the separate regions of the first matrix material tend to remain adhered to the fiber sub-units upon separation thereof. In this way, identifying indicia or markings printed on or otherwise provided on or in the separate regions of first matrix material tend to remain with the respective fiber sub-units. Preferably, the first matrix material has a higher modulus of elasticity than the second matrix material.
Yet another aspect of the present invention facilitates the identification of individual optical fibers within an optical ribbon. To this end, an optical ribbon in accordance with a preferred embodiment of the invention comprises a plurality of optical fibers arranged generally parallel to one another in a generally planar array, and a matrix covering that encapsulates and binds together the optical fibers, the matrix covering comprising a plurality of different colored regions formed of a first matrix material and bound respectively to the plurality of optical fibers for identifying the optical fibers. The matrix covering further comprises a second matrix material that intercedes between and maintains the colored regions substantially separate from one another. The first matrix material adheres to the optical fibers with a greater tenacity than the second matrix material, whereby the colored regions tend to remain adhered to the optical fibers. Preferably, the colored regions extend to and form part of an outer surface of the matrix covering. The optical ribbon can be manufactured by substantially simultaneously extruding the first and second matrix materials over the fibers. Thus, non-colored optical fibers can be colored and ribbonized in one step.